Card file assemblies are well known and commonly used in many environments, including onboard commercial jet airplanes. Card file assemblies house daughter cards that include a male connector block located along an edge of the card that mates with female connectors mounted on a mother board located at the back of the card file when a daughter card is properly inserted. The replaceable daughter cards used on airplanes are sometimes referred to as line replaceable units (LKUs). Daughter cards are installed in card files by inserting the cards into slots formed in the card file chassis and pressing the cards rearwardly until the card connector mates with the card file's mother board connectors. The mating forces of high-pin-count, low-insertion-force connectors can be up to 35 pounds. As a result, it is difficult to assess the point at which connector engagement is complete. Incomplete connector engagement can result in the appearance of a card failure when none has occurred. The likelihood of card failure appearances is particularly true with card files located in a vibration environment, such as onboard an airplane.
Incomplete connector engagement can occur in several ways. Card connections may be incompletely mated or, even though initially fully mated, card connections can become demated when exposed to vibration and shock, such as occurs onboard an aircraft.
In order to overcome the incomplete initial mating and demating problems briefly described above, card retention devices have been developed. Previously developed card insertion and retention devices have a variety of problems and disadvantages. Many daughter card insertion and retention devices require special tools to remove and install a card. Obviously, if an installer does not have the correct tool readily available, time (which is at a premium in an airline environment) is required to find the tool before a card can be replaced. Tolerance buildup in card insertion and retention devices that can result in a significant gap between mated connectors, which can compromise electrical integrity, is another problem associated with prior art card insertion and retention devices.
With respect to connector mating force, a number of attempts have been made to handle the large forces often required to ensure complete connector engagement when a daughter card is inserted into a card file. The prior attempts can be broken into two groups.
One group includes lever-like devices that provide a 4:1 or greater mechanical advantage during card insertion. See, for example, U.S. Pat. No. 4,914,552, entitled Printed Circuit Board Installation and Retaining Apparatus, by Robert P. Keemer; U.S. Pat. No. 4,947,289, entitled Latch Mechanism for a Plug-in Cartridge or the Like, by Ernest R. Dynie; U.S. Pat. No. 5,293,303, entitled Circuit Board Injector/Ejector Device For a Circuit Board Enclosure, by Neil C. Fletcher et al.; U.S. Pat. No. 5,396,401, entitled Modular Printed Circuit Board Holder Structure, Capable of Engaging, In Drawer-Like Fashion, In a Rack of an Electronic Installation, by Girard Nemoz; U.S. Pat. No. 5,398,164, entitled Printed Circuit Card Latching and Stiffening Assembly, by Walter A. Goodman et al.; and German Offenglegungsschfifi DE 41 05 948. The major problem associated with the lever arm devices is that they can easily produce an excessive connector mating force, which can result in the breaking of connector contacts or overcoming a connector's mechanical key features designed to prevent a card from being installed in an incorrect slot.
The second group consists of fasteners, which are captive at both ends of a bracket mounted to a daughter card. The connectors are drawn together and become mated as the fasteners are secured to receptacles on the card file. Like lever arm devices, fasteners can produce excessive forces that can result in the breaking of contacts and/or the overcoming of a connector's mechanical key features if a card is installed in an incorrect slot.
A variety of other approaches have been proposed to positively retain daughter cards in a card file. One approach is to modify lever arm devices of the type described in the foregoing patents by adding a spring-loaded clip to the end of the lever arm. As the card is being installed with the lever arm, the jaws of the spring clip open and close to engage a roll-pin installed in the card. Once engaged, the lever is prevented from opening, thus preventing the card from backing out. One of the disadvantages of this approach is that a connector gap can exist, due to tolerance buildup, when the jaws are engaging the roll-pin. In addition, this approach has the disadvantages of the lever ann devices described above.
Another approach consists of providing the card file with a reinforced front cover with strips of stiff robber padding secured to the inside of the cover. The cover padding provides positive card retention when the cover is closed and the padding is in contact with the outer edges of installed cards. That is, when the cover is closed, the padding impinges on the cards and, thus, prevents the cards from backing out of their related file slots. The problem with this approach is that the rubber padding can take on a permanent set (i.e., remain deflected after load is removed) over time. If this occurs, and a card with a length at the upper end of the tolerance range is replaced with a card at the lower end, a gap will exist between the outer end of the card and the rubber padding when the cover is closed. The gap will allow the card to back out, transferring the gap to the previously mated connectors.
A variation on the foregoing approach is to eliminate the rubber pad and rely on the front cover for card retention. This approach requires designing an allowable nominal gap between the card and the cover. The problem with this approach is that, if one or more card connectors have not been fully seated when the cover is closed, contact between the outer edge of the cards and the cover may result in damage to the cards or the cover, or both.
The present invention is directed to providing a card retention latch that overcomes the disadvantages of prior art card retention mechanisms of the type described above and of other types of card retention mechanisms, such as the one described in U.S. Pat. No. 3,245,546, entitled Self-Locking Handle, by W. B. Stuhler.